Tactical Tracking System

This page describes a Tactical Tracking System for high altitude balloons – or any other object – based on the Automatic Position Reporting System (APRS). The term Tactical Tracking here refers to real-time tracking and chasing, where the coordinates of the tracked object are received in real time and sent to a car navigation unit that is able to dynamically update the target coordinates.

The tracking system is based on APRS. Therefore it has many years of heritage and can take advantage of an existing global APRS network. It does not require any R&D since all components are available off-the shelf and even complete turn-key solutions are available.

In addition to position reporting, the system can also transmit telemetry read via analog and/or digital inputs.

Functional Overview

The transmitter placed on-board the balloon. It transmits GPS coordinates and other telemetry at regular intervals.

The global APRS network that receives the APRS packets from the balloon via digipeaters and publishes them on the global APRS network, see http://aprs.fi/

A mobile APRS receiver station that is used for real time tactical navigation in the field where no Internet is available. This station also receives the APRS packets directly from the balloon.

Diagram

Electrical Architecture

Transmitter

GPS Receiver

OpenTracker+ SMT

The OpenTracker+ is an open source APRS tracker that receives NMEA data from a GPS receiver, encodes it into APRS packets and generates AFSK signal suitable for audio input to an FM transmitter. It can also transmit telemetry data that is read from the built-in temperature sensor (non-SMT version) as well as the available ADC channels.

OpenTracker+ can be purchased assembled and tested or as a kit. Additionally, there is an SMT version, which is the one we are using. The SMT version does not include a built-in temperature sensor or LEDs.

Specifications for SMT version

Operating modes

1200 bps AFSK (RX and TX)

300 bps AFSK, PSK31 (TX only)

Supply voltage

DC 6.5 to 28V unregulated or 5V DC regulated

Current consumption

8 mA idle, 20 mA transmitting

Size

31x18x5 mm (24-pin DIP footprint)

Weight

Operating temperature

GPS interface

NMEA in/out

Mechanical interfaces

Pin-header or wire

Special features

Max 200 mA @ 5 V available for GPS

Source code released under Modified BSD license

8-bit analog TM from ADC1-5

digital TM for T1CH1 and ADC6-9

Pinout

Pin

Name

Function

Utilisation

1

5VIN

Regulated 5-volt input

2

RXD

RS-232 data in (from GPS or computer)

3

1WIRE

Dallas 1-wire bus for external sensors

4

AOUT

Audio out to radio

5

ADC5

Analog input

6

T1CH1

Timer channel

7

ADC6

Analog input

8

RST

Reset (active low)

9

ADC7

Analog input

10

IRQ

Transmit-now, profile select, or counter

11

ADC8

Analog input

12

ADC9

Analog input

13

AIN

Audio input from radio

14

ADC4

Analog input

15

ADC3

Analog input

16

TXD

RS-232 data out

17

RED

Red LED output

18

GREEN

Green LED output

19

ADC2

Analog input

20

ADC1

Analog input

21

PTT

Push-to-talk signal to radio

22

REGOUT

Regulator output - 5 volts

23

GND

Ground

24

REGIN

Regulator input - 6.5 to 28 volts

Resources

SRB MX146 FM Transmitter

TBC whether we use 5V or 8V version

The MX146 is an embeddable VHF transmitter module from SRB Electronics. It's programmable for any frequency from 144-148 MHz in 2.5 kHz steps, or it can be used on one of 16 pre-programmed frequencies.

Power output is 500 mW minimum, and typically closer to 850 mW. It draws under 1 mA in standby, has a fast wake-up time (< 25 ms) and is suitable for voice or data with bitrates up to 10 kbps or more.